System for high-frequency heating of work pieces



July 28, 1959 L. BLOK ETAL 2,895,936

SYSTEMYFOR HIGH-FREQUENCY HEATING OF WORK PIECES Filed Feb. 24, 1956 2 3u. 2 EA c ED INVENTOR LQURENS m GOOTZEN ZWPNENUQG AG NT United StatesPatent SYSTEM. FOR HIGH-FREQUENCY HEATING OF WORK PIECES Laurens Blokand Gooitzen Zwanenburg, Eindhoven, Netherlands, assignors, by mesneassignments, to North American Philips Company, Inc., New York, N.Y., acorporation of Delaware Application February 24, 1956, Serial No.567,576

Claims priority, application Netherlands March 3, 1955 2 Claims. (Cl.266-4) The invention relates to. a system for high-frequency heating ofwork pieces. More particularly;.the' invention relates to a highfrequency heating system comprising a time switch to be operated by astartingwontact in order to heat the work piece for a limited period oftime and, moreover, cooling means having a switchingdevice for therelease of cooling fluid to cool the work piece with a certain time lagrelative to the closureof the: starting contact. The cooling fluid mayconstitute, for example, a water jet applied subsequent to the thermaltreatment.

The invention has for its object to materially simplify the control ofthe systems referred to above.

In accordance with the inventiomthe: system is provided with such acoupling between thestartingecontact circuit and the cooling switchingdevice that the release or non-release of the cooling fluid depends uponthe closure time of the starting contact being shorter or longer thanthe said time lag.

In order that the invention may be readily carried into effect, it willnowbe described more fully with reference to the following drawing,wherein: V

Fig. 1' is a schematic diagram of one embodiment of the system accordingto the invention in a perspective view;

Fig. 2 is a schematic diagram of an embodiment of a timing circuit whichmay be utilized in the system of Fig. 1; and

Fig. 3 is a schematic diagram ofan embodiment of a relay circuit whichmay be utilized in the system of Fig. 1.

The system shown in Fig. 1 is constituted by a highlfrequency furnacehaving a feed -back'electrontube oscillator, which is housed in a metalcasing 1. The highfrequency furnace is preferably constructed asdescribed in US. Patents 2,756,314, issued July 24, 1956 to Blok, and2,773,192, issued December 4, 1956 to -Blok' et' al.

The front panel of the casing 1' is provided with. a plate 2 ofinsulating material, through which theoutput conductors 3, 4 of thehigh-frequency furnace are taken to the outside. To these outputconductorsi'i, 4 is connected a working coil 5. The working coil 5surrounds a work piece 6 to be heated, which bears on a working table 7,mounted on the front panel.

In order to control the power transferred to the work piece 6 the frontpanel is provided with a manualcontrol wheel 8, by which the couplingbetween the high-frequency oscillator and the load can be varied bymechanical means, as described for example in U.S. Patent 2,662,162,issued December 8, 1956' to Blok.

The side panels of the casing 1' are provided with air slots 9, and theright-hand side panel is provided with a switching arm 10 to switch onthe supply devicefor the high-frequency generator.

Along the top side of the front panel provision is made of a measuringand control board 11, which is movable in order to render thecontrol-apparatus mounted behind it readily accessible for supervision.

A starting contact S provided on the board 11,

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which is also provided with awattmeter 13 to measurethe output power.

Behind the board 11 provision is made of a time switch 14, which isconnected through a conductor 15 to the connecting terminals of thestarting contact S. The time switch 14 serves to switch on thehigh-frequency heating for a limited period of time. In order to renderthis period adjustable, the time switch 14 is provided with atime-adjusting mechanism 16, the front side of which projects through arecess in the control-board 11, when it is closed, this front side beingthus accessible to the operator.

The time switch 14 may, ofv course, comprise various types of apparatus,one of which types of apparatus may, for example, comprise a mechanicaltimeswitching clock. In the presentcase use is made of an electronictime switch, the details of which will be explained with reference toFig. 2. p

The device comprises furthermore a cooling switching device 18, to beconnected" tothe water mains through a pipe 17, in order to release awater jet through a pipe 19 providedover the work piece.

For the cooling operation the top surface 20 of' the work table 7 isdepressed and provided with slots 21, which open into an 0utlet22;

If the. work piece 6 is only to beheated, the system is. controlled asfollows.

First, bymeans of the time adjusting mechanism 16 of the time switch 14'the desired heating period is adjusted. Then, by transient closing ofthe starting contact S the time switch 14 is operated. The heating isthen switched on and automatically switched out by the time switch afterthe predetermined periodihaselapsed; Then the high-frequency heatedworkpiece is cooled in the natural way..

If it. is desired to apply a forced cooling to the work piece, thestarting'contact S. isnot. only closed'transiently, as in the aforesaidcase, but it is kept closed, so that the cooling switching device 18,.after a period determined by a delay device 23, is excited automaticallythrough a conductor 24. p

The delay device 23; as well as thetime switch'14, is connected throughthe conductor 15" to the connecting terminals of the starting contact S.The delay device 23 is preferably adjustableand may, for example, beconstituted by a relay of known type, responding with time lag, forexample a thermal relay or a switching clock work. As an alternative,use may bemade of an e'lec tronic delay device, for example", a"suitable trigger circuit (one-short multivibrator).

Since, in principle, in the system shownin Fig. 1 the] heating periodand the delay 'before'switching on the cool ing fluid are independent ofone another, it is possible to: cool forcedly the work piece duringthelast part of the heating period; This may be desired, forexample fortempering;

If a forced cooling is only' desired immediately after the heatingoperation, the control-apparatus 14, 23, 18 may be simplified by'usingthetime switch 14at the same time as a delay device. The timeswitch 1'4is-connected, in this case, through the conductor 25- (shown in brokenlines in Fig; 1') to the cooling switching device1 8 and the delaydevice 23 is dispensed with. p p p Figs. 2 and 3 are detailedembodiments of apparatus which are very suitable inpractice. p i i Fig.2 is a timing circuit of known type, constructed as a multivibrator witha single stable: operational posivia a contact (not shown).

shown), via the energizing winding of a time-switch relay B and aworking contact a of a switching relay A to be described hereinafter,this relay switching on, upon excitation, the high-frequency heating'forthe work piece The time-switch relay B keeps a holding circuit ofthe'switching relay A closed by means of a working contact b for theduration of the energization.

r The control-grid of the triode 27 is connected, for direct-currentfeed-back, to a tapping point of a potentiometer with resistors 32, 33and 34 connected between the anode of triode 28 and ground. The anode oftriode 28 is connected via an anode resistor 35 to the anode voltagelead 31. Between the anode voltage lead 31 and ground provision is madeof a potentiometer having resistors 36 and 37. The control-grid oftriode 28 is connected on the one hand via an adjustable resistor 39 tothe junction 38 of the potentiometer resistors 36, 37

and on the other hand via a capacitor 40 to a variable tapping point ofthe cathode resistor 29. The capacitor 40 is shunted by a rest contact[2 of the time-switching relay B in series with a resistor 41.

With a suitable choice of the control-grid voltage ap plied to thecontrol-grids of triodes 27 and 28 the triode 27 is cut off in the restposition of the multivibrator described above and the triode 28 drawscurrent. upon the energization of the switching relay A, the workingcontact a is closed, the anode of triode 27 starts to take current, sothat, as is known, a relaxation is produced and the multivibratorchanges over into the socalled operational position, in which the triode27 takes the full anode current and the triode 28 is cut ofi by negativegrid bias voltage.

When the triode 27 is conductive, the time-switching relay B included inthe anode circuit thereof is energized and the rest contact b is open.The capacitor 40 included in the control-grid circuit of triode 28 isthen no longer shunted by the resistor 41, so that the triode 28 canbecome conductive only with a time lag determined by the charging timeconstant of the capacitor 40. The charging time constant of thecapacitor 40 can be controlled coarsely to adjust the desired heatingperiod by means of the variable resistor 39 and finally by theadjustment of the tapping point on-the cathode resistor 29. At thetermination of the adjusted time, the triode 28 starts taking current,the multivibrator flops back into the rest position, the time-switchingrelay B is deenergized and the rest contact b is closed.

In order to render therest position of the triode 27 independent oftemperature fluctuations, the resistor 32 of thepotentiometers 32, 33,34 is shunted by a resistor 42 with negative temperature coetficient.

Fig. 3 is a relay circuit arrangement for use in conjunction with thetime switch shown in Fig. 2, this arrangement being connected toterminals 43 and 44 of an alternating-current source for energization ofrelays. This relay arrangement includes the starting contact S,described with reference to Fig. 1, a switching relay A (referred toabove) with working contacts a and a;,, working contacts b b and restcontact b., of the timeswitching relay B of Fig. 2, an auxiliary relay Cwith a change-over contact and a working contact 0 and finally a coolingrelay D, which forms part of the cooling switching device 1801:" Fig. 1and which, upon energization, opens a valve (not shown in the figures)to release the cooling fluid.

In the rest position none of the relays A to D is enengized and therelay contacts shown in Figs. 2 and 3 occupy the positions shown.

The relay arrangement becomes operative by depressing and hence closingthe starting contact S. The starting contact S completes theconventional energizing circuit of switching relay A via the change-overcontact c When the switching relay A is energized, the working cona, anda are closed. and the high-frequency heating When,

current is switched on by means of a working contact (not shown).

The closure of the working contact a prepares a holding circuit for theswitching relay A, this holding circuit including a working contact b ofthe time-switching relay B. p 7

By closing the working contact a included in the anode circuit of thetriode 27 of the time-switch shown in Fig. 2, thetime-switching relay Bis energized in the manner described above for a predetermined period.Thus the contacts b b 12 are changed over.

The working contact b completes the holding circuit of the switchingrelay A, already prepared by the working contact a so that upon releaseand thus opening of the starting contact S, or after the change-overcontact c has been changed over into the working position, the switchingrelay A remains energized via an interruptor 45 (to be describedhereinafter) and the working contacts a and 12 The working contacts bcompletes the energizing circuit of the auxiliary relay C via the pushbutton 45 and the working contact a so that auxiliary relay C isenergized, the change-over contact 0 is movedinto the working positionand the working contact 0 is closed. The change-over of the contact 0into the working position results in the completion of a holding circuitfor the auxiliary relay C. This holding circuit extends from theterminal 43, via the starting contact S, the change-over contact in theoperational position, and the energizing winding of the auxiliary relayC to the terminal 44. The working contact a; results in the preparationof the energization of the cooling relay D.

The closure of the starting contact S thus results, as is described, inthe energization of the relays A, B and C in a rapid order ofsuccession. The cooling relay D is not yet energized.

If the starting contact S is closed only transiently i.e. for a timeshorter than the duration determined by the time switch, the time switchis operated by means of the switching relay A and the relays B and C areenergized. When the time-switching relay B is deenergized, all relaycontacts return into the positions shown, since the working contacts band b open the holding circuit of the switching relay A and the normalenergizing circuit of the auxiliary relay C respectively. Thus, upon atransient closure of the starting contact S the work piece to be treatedis only heated, since the cooling relay D is not energized.

However, if, subsequent to its closure, the starting contact S is keptclosed, the deenergization of the timeswitching relayB results it istrue, again in the deenergization of the switching relay A, but theauxiliary relay C remains energized via its holding circuit includingthe starting contact S and the change-over contact 0 in the workingposition. The working contact c in the energizing circuit of the coolingrelay D remains closed. When, upon deenergization of the time-switchingrelay B, the rest contact b returns into the rest position (terminationof the heating of the work piece), the energizing circuit of the coolingrelay D is closed. Relay D is thus energized, so that the water currentflows until the starting contact is released.

Thus, when the starting contact S is kept closed, the work piece isheated and immediately thereupon a forced cooling of thework piece isautomatically obtained.

The system described above may be constructed for manual operation in asimple manner. In such a case the time switch is not operated. To thisend, the system is provided with an auxiliary switch, which, upon beingchanged over from the time-switch position T into the manual position H,interrupts the anode voltage le ad of the time switch via a contact 46in Fig. 2 and shunts the working contact b in the holding circuit ofswitching relay A by means of a contact 46' in Fig. 3.

By a transient closure of starting contact S the switching relay A isenergized and remains energized via its holding circuit. Thehigh-frequency heating is then switched on by means of the workingcontact (not shown and referred to above) of switching relay A. In orderto terminate the heating, the holding circuit of the switching relay Aincludes the interrupter 45.

While the invention has been described by means of a specific exampleand in a specific embodiment, we do not wish to be limited thereto, forobvious modifications will occur to those skilled in the art withoutdeparting from the spirit and scope of the invention.

What is claimed is:

1. High frequency heating apparatus for heating a work piece, comprisingswitching means for applying heating energy to said work piece for apredetermined period of time, cooling means for applying a coolingmedium to said work piece, means for starting the operation of saidswitching means and said cooling means, and means comprising saidswitching means for delaying the operation of said cooling means for apredetermined period of time after the actuation of said starting meansupon continuous actuation of said starting means, and for preventing theoperation of said cooling means upon actuation of said starting meansfor an interval less than said last-mentioned period of time.

2. High frequency heating apparatus for heating a Work piece, comprisingswitching means for applying heating energy to said work piece for apredetermined period of time, said switching means comprising a timeswitching relay having a working contact and a rest contact and meansfor energizing said time switching relay during the application of saidheating energy, cooling means for applying a cooling medium to said workpiece, means for starting the operation of said switching means and saidcooling means, and means comprising said switching means for delayingthe operation of said cooling means for a predetermined period of timeafter the actuation of said starting means upon continuous actuation ofsaid starting means and for preventing the operation of said coolingmeans upon actuation of said starting means for an interval less thansaid last-mentioned period of time, said last-mentioned means comprisingan auxiliary relay having a holding contact and a Working contact, meansfor energizing said auxiliary relay including the working contact ofsaid time switching relay and means for holding said auxiliary relayenergized including the holding contact of said auxiliary relay inseries circuit arrangement with said starting means, said cooling meanscomprising a cooling relay and means for energizing said cooling relayincluding the rest contact of said time switching relay and the workingcontact of said auxiliary relay in series circuit arrangement with saidstarting means.

References Cited in the file of this patent UNITED STATES PATENTS

